Company

Stealth BioTherapeutics

Last reviewed: 2026-10-19

Scores have not been assigned.

Source Summary

7 reviewed sources across 3 source categories.

Regulatory sources4
Trial registries2
Original scientific reports1

Company Snapshot

Company / scope Original accelerated approval: Barth syndrome, adult and pediatric patients weighing at least 30 kg.

Evidence review date 2026-10-19

Event dates and registry update dates remain distinct.

Program context FDA approved FORZINITY (elamipretide) under accelerated approval on 19 September 2025 to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg. The applicant was Stealth BioTherapeutics Inc.

Executive Summary

Stealth BioTherapeutics is the applicant named in the original FORZINITY approval. This elamipretide product received US accelerated approval on 19 September 2025 to improve muscle strength in adults and children with Barth syndrome who weigh at least 30 kilograms. The approved indication is specific to that disease and population.

Why It Matters

The company offers an example of a mitochondrial therapeutic reaching a narrow regulatory indication with explicit evidence conditions. That does not establish a treatment for normal aging. The next material evidence is confirmation of patient benefit in the relevant population and continued safety follow-up, assessed separately from earlier failed studies.

Platform / Pipeline Overview

Program	Mechanism / pathway	Stage / status	Source type	Evidence boundary	Caution note
Elamipretide / FORZINITY		US accelerated approval: Barth syndrome, adult/pediatric patients weighing at least 30 kg	FDA approval letter / FDA prescribing information / Original scientific article / Sponsor-submitted trial registry	Randomized walking/fatigue primary endpoints failed; knee-strength findings came from the open-label extension.	Confirmatory clinical benefit remains required. MMPOWER-3 is a separate failed study.

Related Trials

Registry ID	Status / phase	Relationship	What it supports	What it does not prove
NCT03098797	Barth study; randomized portion and open-label extension	The Barth study randomized 12 participants. Elamipretide was not superior to placebo on its randomized walking-distance and fatigue primary endpoints; increased knee-extensor strength was observed in the open-label extension, not the randomized portion.	The specific trial identity, design or dated status cited in this profile.	The Barth indication does not establish treatment benefit for normal aging or overturn a separate primary-mitochondrial-myopathy trial result.
NCT03323749	Terminated; separate primary mitochondrial myopathy study	MMPOWER-3 (NCT03323749) randomized 218 people with primary mitochondrial myopathy and did not meet either walking-distance or fatigue primary endpoint at 24 weeks. The registry is terminated and gives failure of the double-blind primary endpoints as its stop reason.	The specific trial identity, design or dated status cited in this profile.	The Barth indication does not establish treatment benefit for normal aging or overturn a separate primary-mitochondrial-myopathy trial result.

Timeline / Milestones

2025-05-15 Earlier complete response letter FDA integrated review of elamipretide NDA 215244 / FDA original FORZINITY approval letter, NDA 215244
FDA review records a complete response letter on 15 May 2025 before the August resubmission and September approval.
2025-09-19 Indication-limited accelerated approval FDA FORZINITY prescribing information / FDA original FORZINITY approval letter, NDA 215244
FDA approved FORZINITY (elamipretide) under accelerated approval on 19 September 2025 to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg. The applicant was Stealth BioTherapeutics Inc. The accelerated indication rests on knee-extensor muscle strength as an intermediate clinical endpoint. Continued approval may depend on confirmation of clinical benefit.

Source Posture

Source class

Regulatory sources

Original agency review; distinct from issuer-reported regulatory history.

Source class

Trial registries

Sponsor-submitted design/status metadata; posted or completed status does not establish efficacy.

Source class

Original scientific reports

Original results abstract checked. Peer review does not establish independent replication.

Interpretation

Editorial interpretation

The Barth indication does not establish treatment benefit for normal aging or overturn a separate primary-mitochondrial-myopathy trial result.

Evidence / Claim Boundary

Evidence and limitations

What supported the decision

The indication rests on knee-extensor muscle strength, an intermediate clinical endpoint. In the 12-participant Barth study, the randomized portion did not show superiority over placebo on the walking-distance and fatigue primary endpoints. Increased knee-extensor strength appeared during the open-label extension, rather than during the randomized comparison. Those limitations belong beside the approval.

Evidence and limitations

Approval and remaining evidence

FDA requires a confirmatory trial to verify clinical benefit. Its review also records an earlier complete response letter in May 2025, before the later approval. The application metadata checked for this profile continues to link the original approval and September 2025 labeling; this review does not establish that confirmatory benefit has been demonstrated. The label includes injection-site reactions and potentially serious hypersensitivity reactions.

Evidence and limitations

A different disease, a different result

MMPOWER-3 studied 218 people with primary mitochondrial myopathy. It did not meet either its walking-distance or fatigue primary endpoint at 24 weeks, and its registry record is terminated. That result remains part of elamipretide’s history. It is a separate trial in a separate disease setting from the Barth approval.

What This Does Not Prove

Editorial interpretation

Evidence limits

The Barth indication does not establish treatment benefit for normal aging or overturn a separate primary-mitochondrial-myopathy trial result.

Detailed Sources

View detailed source table

Regulatory sources

Source	Type	Supports	Limitation	Link
FDA integrated review of elamipretide NDA 215244	FDA review document	Original regulatory review and earlier complete response history.	Original agency review; distinct from issuer-reported regulatory history.	Original source
FDA FORZINITY prescribing information	FDA prescribing information	Approved population, randomized versus open-label evidence and safety warnings.	Original prescribing information; preserve the exact indication, evidence limitations and safety warnings.	Original source
FDA application metadata for NDA 215244	FDA application metadata	Original application entry and linked September 2025 label.	Application metadata and linked original documents; not proof of completed confirmatory benefit.	Original source
FDA original FORZINITY approval letter, NDA 215244	FDA approval letter	Exact accelerated approval and confirmatory requirement; prior regulatory action history.	Original approval letter; requirements and planned milestones do not establish completed confirmatory benefit.	Original source

Trial registries

Source	Type	Supports	Limitation	Link
NCT03323749 original trial record	Sponsor-submitted trial registry	Exact trial design and dated registry status. 2022-01-24	Sponsor-submitted design/status metadata; posted or completed status does not establish efficacy.	Original source
A Trial to Evaluate Safety, Tolerability and Efficacy of Elamipretide in Subjects With Barth Syndrome	Sponsor-submitted trial registry	Exact trial design and dated registry status. 2024-04-16	Sponsor-submitted design/status metadata; posted or completed status does not establish efficacy.	Original source

Original scientific reports

Source	Type	Supports	Limitation	Link
Karaa et al. MMPOWER-3 randomized trial	Original scientific article	Separate MMPOWER-3 primary-endpoint failures.	Original results abstract checked. Peer review does not establish independent replication.	Original source

Confidence / Methodology

Editorial status

Confidence

Bounded source-reviewed profile; independent specialist clearance is not implied.

Scope

Methodology note

Facts and registry labels checked as of 2026-10-19. Company disclosures, trial records, original scientific reports and regulatory documents are identified by source type below. Editorial interpretation is distinct from a demonstrated treatment result.

Freshness

Last reviewed

2026-10-19